Humidity controller with thermal relay



April 4, 1967 c. E. MARKHAM 3,312,398

' HUMIDITY CONTROLLER WITH THERMAL RELAY Filed June 28, 1965 atomizer.

United States Patent Ofiice 3 ,3 l2,398 Patented Apr. 4, 197

This invention concerns means for controlling the amount of moisture tobe supplied to a space in accordance with the requirements to maintainsome preselected moisture content of the air in the space.

The object of the invention is to provide a simple and reliable humiditycontroller employing a moisture sensing element of the type in which thecontraction and relaxation of an organic material in response todecreasing and increasing moisture content of the ambient air providesmotion to effect operation of control means and in which the workrequired of the sensing element in the performance of its controlfunction is reduced to a negligible amount thereby to preclude permanentdistortion of the organic material and consequent drift of the controlpoint.

Other objects and advantages will appear from the following descriptionwhen read in connection with the accompanying drawing.

The single figure of the drawing is a schematic view of a humiditycontroller constructed in'accorda-nce with the present invention.

Referring to the drawing, a humidifier or moisture supply means isgenerally indicated at and includes a normally closed solenoid valve 12interposed in a water supply line 14 and an electric motor 16 fordriving an The humidifier supplies moisture to a space in which amoisture responsive switch generally indicated at 18 is located. Switch18 comprises a moisture sensing element consisting of a thin, flexible,formed metal strip 20 having a thin strip of organic material 22 gluedthereto. The strip 22 may be wood, paper formed of wood pulp or otherorganic fibres, or a suitable synthetic plastic material. Theconstruction and operation of this type of moisture responsive elementis well known. It is also well known that when this type of element isconstructed to such dimensions that it responds rapidly and considerablyto changes in the moisture content of the ambient air it is unable toperform any appreciable amount of work in response to slight changes inthe moisture content of the air. Moreover, it is well known that anyappreciable stressing of elements of this type in the performance of thecontrol function results in a distortion of the organic material and aconsequent drift of the control point.

The laminated strip 20-22 is coiled at one end and fixed in a slot intheend of rotatably adjustable stud 24. Stud 24 has an arm 26 attachedthereto which sweeps an indicia plate 28 and provides means to rotatablyadjust the stud. At its free end the metal strip 20 carries a contact 30arranged to cooperate with a threadedly adjustable fixed contact 32.Metal strip 20 also carries an armature 34 adjacent its free end, and asmall electromagnet 36 mounted adjacent the armature operates whenenergized to pull the free end of strip 20 downward. The straightportion of strip 20-22 is shown illustrated in a horizontal position;however, it may be mounted in a vertical position in order to precludethe influence of gravity.

A thermal relay is generally indicated at 38 and includes a resistanceheater 40 and a bimetal switch blade 42 arranged in good heat transferrelationship with resistance heater 40. The bimetal blade 42 is anchoredat one end in a support 44 and carries movable contacts 46 and 48 onopposite sides of its free end. The movable contacts 4 6 and 48cooperate with threadedly adjustable fixed contacts 50 and 52,respectively. A snap action of relay 38 between its opposite positionsof closure with fixed contacts 50 and 52 is accomplished by theprovision of a pair of permanent magnets 54 and 55 arranged to attractarmature pieces 56 and 57, respectively, carried by the free end ofbimetal blade 42. The arrangement of the greater and lesser expandingmetal strips of bimetal blade 42 is such, and the blade is so preformed,that at normal room temperatures it assumes the position shownin thedrawing with contacts 46-50 closed and contacts 48-52 open, and whenheated to a predetermined temperature by resistance heater 40, it warpsto the left separating contacts 46-50 and closing with contacts 48-52.

The resistance heater 40 is connected across a pair of power sourceterminals 58 and 60 through a lead 62, the

metal strip 20, contacts 30-32, a lead 64, a lead 66, a

lead 68, contacts 50-46, bimetal blade 42, and a lead 70. The normallyclosed solenoid valve 12 is connected in parallel with motor 16 by leads82 and 80, and both are connected across power source terminals 58-60through lead 76, a lead 78, thermal relay contacts 48-50, bimetal strip42, and lead 70. The resistance heater 40 has sufficient heat outputwhen energized to effect the heating of bimetal strip 42 to itsoperating temperature at a relatively rapid rate.

In operation, when the moisture content of the air ambient to the switch18 falls below that preselected to be maintained, the strip of organicmaterial 22 shrinks, causing contacts 30-32 to close. This contactclosing force efiected by the response of coiled strip 20-22 will bevery light, but will be sufficient to at least partially energize thesmall electromagnet 36 which will, in turn, immediately increase thecontact pressure at contacts 30- 32 so as to effect full energization ofthe parallel connected resistance heater 40 as well as theelectromagnet. When this occurs bimetal blade 42 will be heated at arapid rate and will, at a predetermined temperature, have built upsufficient force due to warping to pull away from the attraction ofmagnet 54, thereby opening contacts 46- 50 and closing contacts 48-52with a snap action. In this position the free end of the bimetal stripis attracted by magnet 55 which provides immediate strong contactpressure between contacts 48-52 and maintains this pressure untilsufficient warping of the bimetal strip in the opposite direction, uponcooling, builds up suflicien-t stress to pull away from magnet 55 andreturn to the position shown.

The opening of contacts 46-50 de-energizes resistance heater 40 andelectromagnet 36, and the closing of contacts 48-52 completes thedescribed circuit energizing the parallel connected motor 16 andsolenoid 12, thereby supplying moisture to the air ambient to switch 18.Deenergization of electromagnet 36 releases the free end of strip 20-22so that this sensitive element is now again entirely free to respond toan increase in the moisture content of the ambient air effected byoperation of humidifier 10. De-energization of resistance heater 40permits the bimetal strip to cool to normal room temperature, whichresults in its snap action return to the position shown in the drawing.Upon cooling, the permanent magnet 55 prevents movement of the free endof bimetal strip 42 until the strip has cooled considerably below thetemperature to which it was heated by resistance heater 40.

Inasmuch as the resistance heater 40 has the capacity to heat thebimetal blade rapidly, the time-temperature curve upon heating risesabruptly until the operating temperature of the blade in one directionis reached. On the other hand, upon cooling when the resistance heateris de-energized and in the absence of any cooling means,

the time-temperature curve characteristically flattens out as thetemperature approaches normal room temperature.

The time during which contacts 48-52 are closed is thereforeconsiderably longer than the time required to heat the bimetal blade toits operating point. If contacts 30- 32 remain closed due to aninsufliciency of moisture supplied during one operating cycle of thehumidifier, it will continue its cycles of operation until sufi'icientmoisture is supplied to effect opening of contacts 30-32.

The on time of the humidifier may be increased by any one of a number ofexpedients which slow down the cooling rate of bimetal strip 42. Forexample, the cooling rate of the blade 42 may be slowed down by merelyincreasing its thickness, or by encasing the bimetal strip 42 and heater40 so as to retain the heat, or by providing a heat sink in proximitywith and in heat transfer relationship with the heater 40 and bimetalblade 42. Preferably, the relay 38 is designed so that the timedifferential between heating and cooling of blade 42 is in the order ofone to six so that, when the time required to heat the bimetal bladefrom room temperature to its operating temperature in one direction isthirty seconds, its cool-down time during which the humidifier isoperating is in the order of three minutes.

In the preferred form of the invention, the electrical resistance ofmetal strip 20 and bimetal strip 42 is sufficiently low to preclude anysignificant heating.

Modifications of the illustrated embodiment within the spirit of theinvention will occur to those skilled in the art, .and the use of allsuch modifications is contemplated. For example, an overcenter toggleaction including the bimetal blade 42 as one of the toggle links may besubstituted for the permanent magnets 54 and 55 and armature pieces 56and 57 to effect a snap action. Also, any suitable arrangement of amoisture sensing element employing an organic filament or strip held intension by spring means may be substituted for the glued and' coil metaland organic strips 2fi22 without departing from the spirit of theinvention.

The foregoing description is intended to be illustrative and notlimiting, the scope of the invention being set forth in the appendedclaims.

I claim:

1. In a humidity controller, an electrical power source, an electricallyoperated humidifier, a sensitive humidity responsive switch which closesits contacts in response to decreasing humidity, an electromagnetoperative when energized to increase the closing force applied to saidhumidity responsive switch contacts when they close in response to adecrease in humidity, a double throw heat responsive switch having anormal cold position and an opposite hot position to which it moves whenheated, an electrical resistance heater operative when energized to heatsaid double throw heat responsive switch at a rate which effects itsoperation from its cold to hot position in a considerably shorter timethan is required for it to subsequently cool sufiiciently to effect itsreturn to its cold position when said resistance heater is de-energized,circuit connections including in series arrangement said humidityresponsive switch contacts when closed, said double throw switch in itscold position connecting said electromagnet, and said resistance heateracross said power source, whereby said electromagnet and said resistanceheater are de-energized when said double throw switch moves to its hotposition, and circuit connections including said double throw switch inits hot position connecting said humidifier across said power source.

2. In a humidity controller, a power source, a double throw thermalrelay having a normal cold position and an opposite hot position andhaving one pair of contacts, which are closed when in its hot position,adapted to control the operation of a humidifier and having a secondpair of contacts which are closed when in its cold position, anelectrical resistance heater operative when energized to heat saiddouble throw thermal relay at a rate which effects its operation fromits cold position to its hot position in a considerably shorter timethan that required for it to subsequently cool sufficiently to effectits return to a cold position when said resistance heater isde-energized, a sensitive humidity responsive switch which closes itscontacts in response to decreasing humidity, an electromagnet which whenenergized increases the pressure between the humidity responsive switchcontacts when they are closed, and circuit connections including saidhumidity responsive switch contacts and'said secon-d pair of thermalrelay contacts in series arrangement connecting said resistance heaterand said electromagnet across said power source, whereby said humidityresponsive switch is freed from the influence of said electromagnet whensaid thermal relay moves to its hot position. 1

3. In a humidity controller, a sensitive humidity responsive switchwhich closes its contacts in response to decreasing humidity, anelectrom-agnet operative when energized to increase the pressure betweensaid humidity responsive switch contacts when closed, a double throw,

snap action, thermal relay having a normal cold position and a hotposition and including an electrical resistance heater which whenenergized heats said relay at a rate which effects its operation fromits cold to hot position in a considerably shorter time than is requiredfor it to cool sufiiciently to effect its return to a cool position whensaid resistance heater is de-energized, said double throw relay having afirst pair of contacts which are closed when said relay is in its hotposition and which are adapted to control the operation of moisturesupply means and a second pair of contacts which are closed when saidrelay is in its normal cold position, and circuit connections includingsaid humidity responsive switch contacts and said second pair of relaycontacts in series arrangement for connecting said electromagnet andsaid electrical resistance heater across an electrical power source.

References Cited by the Examiner UNITED STATES PATENTS 435,898 9/1890Johnson 236-78 912,815 2/1909 Cook 236-44 2,181,606 11/1939 Parks 23668ALDEN D. STEWART, Primary Examiner.

3. IN A HUMIDITY CONTROLLER, A SENSITIVE HUMIDITY RESPONSIVE SWITCHWHICH CLOSES ITS CONTACTS IN RESPONSE TO DECREASING HUMIDITY, ANELECTROMAGNET OPERATIVE WHEN ENERGIZED TO INCREASE THE PRESSURE BETWEENSAID HUMIDITY RESPONSIVE SWITCH CONTACTS WHEN CLOSED, A DOUBLE THROW,SNAP ACTION, THERMAL RELAY HAVING A NORMAL COLD POSITION AND A HOTPOSITION AND INCLUDING AN ELECTRICAL RESISTANCE HEATER WHICH WHENENERGIZED HEATS SAID RELAY AT A RATE WHICH EFFECTS ITS OPERATION FROMITS COLD TO HOT POSITION IN A CONSIDERABLY SHORTER TIME THAN IS REQUIREDFOR IT TO COOL SUFFICIENTLY TO EFFECT ITS RETURN TO A COOL POSITION WHENSAID RESISTANCE HEATER IS DE-ENERGIZED, SAID DOUBLE THROW RELAY HAVING AFIRST PAIR OF CONTACTS WHICH ARE CLOSED WHEN SAID RELAY IS IN ITS HOTPOSITION AND WHICH ARE ADAPTED TO CONTROL THE OPERATION OF MOISTURESUPPLY MEANS AND A SECOND PAIR OF CONTACTS WHICH ARE CLOSED WHEN SAIDRELAY IS IN ITS NORMAL COLD POSITION, AND CIRCUIT CONNECTIONS IN-